refactor(desktop): ChatStore structured split + IDB persistence + stream cancel

Split monolithic chatStore.ts (908 lines) into 4 focused stores:
- chatStore.ts: facade layer, owns messages[], backward-compatible selectors
- conversationStore.ts: conversation CRUD, agent switching, IndexedDB persistence
- streamStore.ts: streaming orchestration, chat mode, suggestions
- messageStore.ts: token tracking

Key fixes from 3-round deep audit:
- C1: Fix Rust serde camelCase vs TS snake_case mismatch (toolStart/toolEnd/iterationStart)
- C2: Fix IDB async rehydration race with persist.hasHydrated() subscribe
- C3: Add sessionKey to partialize to survive page refresh
- H3: Fix IDB migration retry on failure (don't set migrated=true in catch)
- M3: Fix ToolCallStep deduplication (toolStart creates, toolEnd updates)
- M-NEW-2: Clear sessionKey on cancelStream

Also adds:
- Rust backend stream cancellation via AtomicBool + cancel_stream command
- IndexedDB storage adapter with one-time localStorage migration
- HMR cleanup for cross-store subscriptions

desktop/src-tauri/src/kernel_commands/skill.rs

@@ -53,6 +53,7 @@ impl From<zclaw_skills::SkillManifest> for SkillInfoResponse {
 ///
 /// Returns skills from the Kernel's SkillRegistry.
 /// Skills are loaded from the skills/ directory during kernel initialization.
+// @connected
 #[tauri::command]
 pub async fn skill_list(
     state: State<'_, KernelState>,
@@ -74,6 +75,7 @@ pub async fn skill_list(
 ///
 /// Re-scans the skills directory for new or updated skills.
 /// Optionally accepts a custom directory path to scan.
+// @connected
 #[tauri::command]
 pub async fn skill_refresh(
     state: State<'_, KernelState>,
@@ -124,6 +126,7 @@ pub struct UpdateSkillRequest {
 }
 
 /// Create a new skill in the skills directory
+// @connected
 #[tauri::command]
 pub async fn skill_create(
     state: State<'_, KernelState>,
@@ -170,6 +173,7 @@ pub async fn skill_create(
 }
 
 /// Update an existing skill
+// @connected
 #[tauri::command]
 pub async fn skill_update(
     state: State<'_, KernelState>,
@@ -214,6 +218,7 @@ pub async fn skill_update(
 }
 
 /// Delete a skill
+// @connected
 #[tauri::command]
 pub async fn skill_delete(
     state: State<'_, KernelState>,
@@ -286,6 +291,7 @@ impl From<zclaw_skills::SkillResult> for SkillResult {
 ///
 /// Executes a skill with the given ID and input.
 /// Returns the skill result as JSON.
+// @connected
 #[tauri::command]
 pub async fn skill_execute(
     state: State<'_, KernelState>,